gcc -g test_execve.c

Without . in PATH
=================
gdb ./a.out
break test_execve.c:11
n until
48         execv(ofile, argv);
(gdb) s
execv (path=0x80489dc "hello", argv=0x804a358) at execv.c:26
26      execv.c: No such file or directory.
        in execv.c
dir /usr/src/kernels/eglibc/eglibc-2.13/posix/
22      /* Execute PATH with arguments ARGV and environment from `environ'.  */
23      int
24      execv (const char *path, char *const argv[])
25      {
26        return __execve (path, argv, __environ);
27      }
(gdb) step
__execve (file_name=0x80489dc "hello", argv=0x804a358, envp=0x804a378)
    at ../sysdeps/mach/hurd/execve.c:30
30      {
(gdb) list
25      int
26      __execve (file_name, argv, envp)
27           const char *file_name;
28           char *const argv[];
29           char *const envp[];
30      {
31        error_t err;
32        file_t file = __file_name_lookup (file_name, O_EXEC, 0);
33      
34        if (file == MACH_PORT_NULL)
(gdb) p file
$42 = 125
35          return -1;
36      
37        /* Hopefully this will not return.  */
38        err = _hurd_exec (__mach_task_self (), file, argv, envp);
[New Thread 27529.6]
warning: "gnu_write_inferior vm_read failed": (os/kern) invalid address
warning: "gnu_write_inferior vm_read failed": (os/kern) invalid address
Can't fetch registers from thread bogus thread id 4: No such thread

With . in PATH
===============
export PATH=.:$PATH
gdb ./a.out
dir /usr/src/kernels/eglibc/eglibc-2.13/posix/
break execve.c:30
(gdb)  p envp[10]
$5 = 0x10265c0 "PATH=.:/sbin:/usr/sbin:/usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games"
(gdb) p file
$11 = 125
[New Thread 27565.6]
warning: "gnu_write_inferior vm_read failed": (os/kern) invalid address
warning: "gnu_write_inferior vm_read failed": (os/kern) invalid address
Can't fetch registers from thread bogus thread id 4: No such thread

gdb ./a.out
dir /usr/src/kernels/eglibc/eglibc-2.13/posix/
break execve.c:38
run
Starting program: /home/srs/DEBs/icon/debugging_icon/a.out 
[New Thread 27569.5]
Can't fetch registers from thread bogus thread id 4: No such thread

restarting again:

dir /usr/src/kernels/eglibc/eglibc-2.13/hurd/
list
34         If TASK == mach_task_self (), some ports are dealloc'd by the exec server.
35         ARGV and ENVP are terminated by NULL pointers.  */
36      error_t
37      _hurd_exec (task_t task, file_t file,
38                  char *const argv[], char *const envp[])
39      {
40        error_t err;
41        char *args, *env;
42        size_t argslen, envlen;
43        int ints[INIT_INT_MAX];
44        mach_port_t ports[_hurd_nports];
45        struct hurd_userlink ulink_ports[_hurd_nports];
46        inline void free_port (unsigned int i)
47          {
48            _hurd_port_free (&_hurd_ports[i], &ulink_ports[i], ports[i]);

(gdb) where
#0  _hurd_exec (task=1, file=125, argv=0x804a358, envp=0x804a378)
    at hurdexec.c:39
...
59        if (argv == NULL)
60          args = NULL, argslen = 0;
61        else if (err = __argz_create (argv, &args, &argslen))
62          return err;
err = 0
63        if (envp == NULL)
64          env = NULL, envlen = 0;
65<-        else if (err = __argz_create (envp, &env, &envlen))
66          goto outargs;
69        for (i = 0; i < _hurd_nports; ++i)
70          if (i == INIT_PORT_PROC && task != __mach_task_self ())
71            {
72              /* This is another task, so we need to ask the proc server
73                 for the right proc server port for it.  */
81          else
82            ports[i] = _hurd_port_get (&_hurd_ports[i], &ulink_ports[i]);
gdb hang here